In recent years, golf wood club heads are fabricated from metal, typically hollow metal heads of a thin shell construction. Exemplary of these are the oversized drivers, fabricated from metals such as stainless steel, aluminum and titanium. Thus, "wood" club heads refer to the class of golf clubs including the driver, typically known as the number one wood, and the fairway woods, typically the number three, four, five and seven woods. The ball-impacting face of the number one wood typically is inclined from the vertical in the range of 71/2 to 12 degrees, while the faces of the fairway woods have a greater inclination, e.g., 13-17 degrees for the number three wood, 20 degrees or so for the number four wood, 23 degrees for the number five wood, and 27 degrees for the number seven wood.
The fabrication of hollow metal wood heads has presented difficulties in achieving high quality parts at reasonable cost. There are several conventional fabrication techniques.
In one fabrication technique, a one piece body structure which does not include the sole plate is made by casting. Because the head body tapers from the center of the head to a smaller sole region footprint where the sole plate opening is located, a multipiece collapsible mold core must be used to cast the body structure. The different pieces of the collapsible interior mold core are then removed through the sole plate opening, and the sole plate is attached to the body structure by conventional techniques, typically welding. Multipiece collapsible mold cores are very expensive, and the set up and removal of the core is time consuming. Moreover, the core pieces can become loose due to mishandling and wear, and this can lead to out-of-tolerance club head wall thicknesses. It is quite difficult to obtain repeatable accuracy using the multipiece core molds, there are problems with the accuracy of sole-plate welding onto the head body, and therefore the yield is low.
Another fabrication technique is to fabricate the club body structure with an integral sole, to which a separate face plate is attached. A face plate opening is provided, through which interior mold core elements are removed after the body structure has been molded. The face plate is then attached to the club head body. While this technique facilitates the molding process, in that multipiece cores having fewer interior core elements may be required than are required for the technique employing interior collapsible cores removed through a sole opening, it suffers the disadvantage of imposing design constraints. The face plate opening must be designed to provide a receiving structure for the face plate, typically a recessed shoulder structure, so that the face plate can withstand the impact stress. Moreover, the face plate is typically attached by welding, and any imperfections in the quality of the welds can lead to failure or performance degradation, since the face is the only part of the wood club head that directly contacts the golf ball.
Accordingly, it would be an advance in the art to have a technique for fabricating hollow metal driver heads, without the need for expensive multipiece mold cores, and which enabled the face plate to be fabricated as an integral part of the club head body structure.